Wideband Code Division Multiple Access, WCDMA, telecommunication systems have many attractive properties that is used for telecommunication services. A specific technical challenge in e.g. WCDMA and similar systems is the scheduling of enhanced uplink channels to time intervals where the interference conditions are favourable, and where there exist a sufficient capacity in the uplink of the cell in question to support enhanced uplink channels. It is well known that existing users of the cell all contribute to the interference level in the uplink of WCDMA systems. Further, terminals in neighbour cells also contribute to the same interference level. This is because all users and common channels of a cell transmit in the same frequency band when CDMA technology is used. The load of the cell is directly related to the interference level of the same cell. The admission control function of the RNC in WCDMA is thus central, since overload results in poor quality of service and unstable cells, behaviours needed to be avoided.
The admission control algorithms need to balance the available resources of each cell or RBS, against the requested traffic by users. This means that important inputs to the admission control algorithms include available HW resources, as well as information on the momentary number of users and their on-going traffic, in each cell.
In order to retain stability of a cell, and to increase the capacity, fast enhanced uplink scheduling algorithms operate to maintain the load below a certain level. This follows since the majority of uplink user channels, at least in WCDMA, are subject to power control. This power control aims at keeping the received power level of each channel at a certain signal to interference ratio, SIR, in order to be able to meet specific service requirements. This SIR level is normally such that the received powers in the radio base station, RBS, are several dBs below the interference level. De-spreading in so called RAKE-receivers then enhance each channel to a signal level where the transmitted bits can be further processed, e.g. by channel decoders and speech codecs that are located later in the signal processing chain.
Since the RBS tries to keep each channel at its specific preferred SIR value, it may happen that an additional user, or bursty data traffic of an existing user, raises the interference level, thereby momentarily reducing the SIR for the other users. The response of the RBS is to command a power increase to all other users, something that increases the interference even more. Normally this process remains stable below a certain load level. In case a high capacity channel would suddenly appear, the raise in the interference becomes large and the risk for instability, a so called power rush, increases. It is thus a necessity to schedule high capacity uplink channels, like the enhanced uplink, E-UL, channel in WCDMA, so that one can insure that instability is avoided. In order to do so, the momentary load must be estimated in the RBS. This enables the assessment of the capacity margin that is left to the instability point.
A particularly useful measure is the uplink (and downlink) cell load(s), measured in terms of the rise over thermal (or noise rise). Rise over thermal (ROT) is defined as the quotient between the momentary wide band power and a thermal noise floor level. All noise rise measures have in common that they rely on accurate estimates of the background noise. Determinations of highly fluctuating power quantities or noise floor according to prior art is typically associated with relatively large uncertainties, which even may be in the same order of magnitude as the entire available capacity margin. It will thus be very difficult indeed to implement enhanced uplink channel functionality without improving the load estimation connected thereto.
At this point it could be mentioned that an equally important parameter that requires load estimation for its control, is the coverage of the cell. The coverage is normally related to a specific service that needs to operate at a specific SIR to function normally. The uplink cell boundary is then defined by a terminal that operates at maximum output power. The maximum received channel power in the RBS is defined by the maximum power of the terminal and the path-loss to the digital receiver. Since the path-loss is a direct function of the distance between the terminal and the RBS, a maximum distance from the RBS results. This distance, taken in all directions from the RBS, defines the coverage.
It now follows that any increase of the interference level results in a reduced SIR that cannot be compensated for by an increased terminal power. As a consequence, the path-loss needs to be reduced to maintain the service. This means that the terminal needs to move closer to the RBS, i.e. the coverage of the cell is reduced.
From the above discussion it is clear that in order to maintain the cell coverage that the operator has planned for, it is necessary to keep the load below a specific level. This means that load estimation is important also for coverage. In particular load estimation is important from a coverage point of view in the fast scheduling of enhanced uplink traffic in the RBS.
Furthermore, the admission control and congestion control functionality in the radio network controller, RNC, that controls a number of RBSs also benefits from accurate information on the momentary noise rise of each cell it controls. The bandwidth by which the RNC functionality affect the cell performance is significantly slower than what was described above, for enhanced uplink scheduling, however, the impacts on cell stability that was discussed above for enhanced uplink are also valid to some extent for the admission control functionality of the RNC.
Admission control assures that the number of users in a cell do not become larger than what can be handled, in terms of hardware resources and in terms of load. A too high load first manifests itself in too poor quality of service, a fact that is handled by the outer power control loop by an increase of the SIR target. In principle this feedback loop may also introduce power rushes, as described above.
The admission control function can prevent both the above effects by regulation of the number of users and corresponding types of traffic that is allowed for each cell controlled by the RNC. A particularly important input to achieve this goal is an accurate estimate of the noise rise of the cell. Hence there is a need for estimation of noise rise in the RNC.
Solutions for the problem to estimate the noise rise are presented in the international patent applications WO 2007/024166, WO 2008/039123 A1 and WO 2011/031193 A1.
Currently, WCDMA networks are experiencing a very fast increase of the uplink traffic levels. The explanation is the introduction of smart phones. These devises both introduce new services that produce upload of large chunks of information, e.g. video clips. They also introduce new low rate signalling. Together, the result is                An increased uplink interference level;        Traffic around the clock (24/7).        
This causes problems for the enhanced uplink, EUL. The reason is that EUL operates by scheduling of users with the target of filling the available interference headroom. This headroom is measured in terms of the rise over thermal, RoT, i.e. the quotient between the total uplink wideband power and the thermal noise floor. The fundamental problem is that when traffic levels remain high 24/7, i.e. 24 hours night and day, the whole week, so does the total received wideband power. The consequence is that it becomes difficult to observe a minimum value that is close to the correct thermal noise floor. Or in other words, that the on-going increase of uplink traffic tend to generate interference 24/7, meaning that there will be no time of day where the traffic is so low that an accurate estimate of the thermal noise power floor can be obtained, by observation of the total wideband received power, as obtained by power estimation of the IQ chip stream from the Radio Unit/Remote Radio Unit RU/RRU. This leads to a too low estimate of the uplink load level, i.e. the RoT. In turn, this leads to scheduling of even more traffic. Eventually this positive feedback may lead to a breakdown of the EUL scheduling and load estimation concept.